To date conveyor belts of reinforced rubber and like materials have been reinforced either with a number of textile fabrics, or with steel wire cables or steel cords provided in the longitudinal direction of the belt. Thereby it is often necessary to provide the textile reinforcement fabrics in a number of layers in order to reach sufficient tensile strength. This generally requires a complicated manufacturing method and apparatus. However, the obtained conveyor belt is rather rigid in the longitudinal direction and turning, respectively driving around drums with a relatively large diameter remains necessary. Moreover, the textile reinforcement is also subjected to a relatively important creep elongation so that it is necessary to tighten the conveyor belt from time to time. The tightening devices require additional space on the conveyor, particularly if used for long conveyor belts. It has already been established for some time that one layer of steel cord or steel cable reinforcement in the longitudinal direction of the conveyor belt suffices to offer the same strength as a multilayer textile reinforcement. See for example British Pat. No. 1,388,785. The conveyor belt is more flexible so that it can be led over small-diameter drums. The creep elongation of steel cord is also much lower. However, it was established that the steel cords must present a structural elongation that is higher than the normal elongation capacity of steel cord to provide the conveyor belt with a given elasticity in normal operating conditions. This requirement was to some extent met by the use of the so-called high-elongation cord, which, however, is an expensive solution.
On the other hand, it is known from the French Pat. No. 1,505,901 to use fabrics with a steel cord warp and plastic weft filaments to reinforce rubber.
It is an object of this invention to provide the steel cords with a suitable elongation capacity by providing the cords mechanically with a zig-zag shape, hereafter called crimp. This solution is more economical than high-elongation cord, particularly since the deformation operation can be carried out in one operation on the preliminarily made steel cord fabric or on the parallel steel cords.
The invention further determines the applicable crimping parameters to obtain a uniform crimp formation without, on the one hand, damaging the steel cords and, on the other, so that the crimped cords have an elongation of 0.3% to 0.8% when loaded to 10% of the steel cord's intrinsic breaking strength.